1. C-Notes: Natural Selection (The Mechanism of Evolution)
Stnd: 8a
C-Notes: Natural Selection (The Mechanism of Evolution)
2/26/2014
Objective:
SWBAT identify how variations of traits play a role in how Natural Selection determines the survival of organisms.

2. Who was Charles Darwin? Proposed a way HOW evolution works
He traveled on a British Ship, called HMS Beagle for 5 years to the Galapagos Islands (1831) and collected a lot of evidence of the natural world (animals and their diversity).
He studied Finches (birds) on their many different beak shapes and sizes.
Wrote a book “The Origin of Species”
Father of Evolution
biblauragraphy.files.wordpress.com
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3. Voyage of the HMS Beagle
mun.ca
Invited to travel around the world
(22 years old!)
makes many observations of nature
main mission of the Beagle was to chart South American coastline
Robert Fitzroy
HMS Beagle

4. Voyage of the HMS Beagle
Voyage of the HMS Beagle
Stopped in Galapagos Islands
500 miles off coast of Ecuador
Field Research on Galapagos Islands…
GoogleEarth: Isla Floreana, Ecuador
3 min video
Galapagos Research Home Video

5. Darwin found…clues in the fossils
Present day Armadillos
blogs.technet.com
Darwin found:
Evidence that creatures have changed over time
Ancient Armadillos weighing 200 lbs!
foxnews.com
Darwin asked:
Why should extinct armadillos & modern armadillos be found on the same continent?

6. Darwin found: Different shells on tortoises on different islands
Darwin asked:
Is there a relationship between the environment & what an animal looks like?
scrapetv.com

7. Darwin’s finches variations in beaks natural selection for most fit
differences in beaks in the original flock
adaptations to foods available on islands
natural selection for most fit
over many generations, the finches were selected for specific beaks & behaviors
offspring inherit successful traits
accumulation of winning traits: both beaks & behaviors
separate into different species
Darwin’s finches
blogs.discovermagazine.com
Why would the finches have developed different beaks?

8. HAWAIIAN finches Like Darwin’s Galapagoes finches…
Evolution of different beaks based on different foods they eat.
Common ancestral finch
ncse.com

9. Earlier ideas on Evolution
LaMarck
evolution by acquired traits
creatures developed traits during their lifetime
give those traits to their offspring
example
in reaching higher leaves giraffes stretch their necks & give the acquired longer neck to offspring
NOT ACCEPTED as valid
fundivision.net
wildlife-pictures-online.com..

10.  Darwin’s view of Evolution Darwin variation selection & survival
giraffes that already have long necks survive better
leave more offspring who inherit their long necks
variation
selection & survival
reproduction & inheritance of more fit traits 

11. people have chosen variations in animals and plants to emphasize and produced plants and animals that are beneficial to humans
What is Artificial Selection? (Selective Breeding)

12. Adaptations What is Natural Selection?
Adaptations are traits that enhance the survival and reproductive success.
All species have genetic variation
traits that help individuals survive
survive predators
survive disease
compete for food
compete for territory
traits that help individuals reproduce
attracting a mate
compete for nesting sites
successfully raise young
What is Natural Selection?
farm3.static.flickr.com
flickr.com
Certain drugs have become popular among teens and young adults at dance clubs and raves.
3.bp.blogspot.com
mesh.biology.washington.edu
Adaptations

13. Survival & Reproduction of the Fittest
Over production. Most organisms produce more offspring than can survive.
Competition. Organisms compete for food and resources.
Variation.
There is variation among individuals of a species.
Adaptation.
Individuals with traits best suited to the environment will survive.
What are the Main Points of Darwin’s Theory on Natural Selection?
Survival & Reproduction of the Fittest

14. How does that work? Variation Over-Production & Competition Adaptation`
Natural Selection
Nature selects the ones that “fit” the environment better … survive & reproduce

15. He developed the Theory of Evolution by Natural Selection “Survival of the Fittest”
He believed that all Variation exist first ….then Evolution
Individual organisms differ genetically; their variations are passed on and inherited through their genes
Why is Evolution by Natural Selection so strongly associated with Darwin?
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16. How does Variation play a role in Natural Selection?
Genetic Variation is a key to Natural Selection
Populations are a mix of different individuals
This variation is caused by recombining genes during meiosis
Variation is the result of ….
Sexual reproduction: how certain genes are passed on due to meiosis. (Meiosis- Crossing over)
Mutations: random changes in a DNA sequence that could have a positive, negative or no effect on an organism’s fitness.
Migration: new individuals join a population and bring in new genes. (genes can move into or out of a population by migration)
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www2.beverlyajackson.com

17. Survival & Reproduction of the fittest
firemice.wordpress.com
msnbcmedia.msn.com
not the biggest…
not the strongest…
not the fastest…
…IT IS the FITTEST!
not the bravest…
pixdaus.com
Adaptations
the traits that help an organism FIT the environment better to
survive & reproduce

18. Evolution explains Unity & Diversity
Only evolution explains both
unity of life
similarities between all living things
diversity of life
wide variety of different creatures on Earth
valeofglamorgan.gov.uk
Diversity of Life on Earth
DNA
Unity of Life on Earth
CELLS

19. A little fun with camouflage…
conservationreport.com
bisbeemedia.com
designboom.com
Insects are experts at camouflage!
Search for more on the internet!
Bill Nye Evolution: First 24:00 minutes.

20. Directional Selection Stabilizing Selection Disruptive Selection
What are the types of Natural Selection?
There are 3 types:
Directional Selection
Stabilizing Selection
Disruptive Selection
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21. What is Directional Selection?
In “directional selection,” natural selection favors a characteristic on the extreme of the phenotypic variation.
directional selection occurs in response to a change in the environment that gives a competitive advantage to a particular phenotype
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22. Examples of Directional Selection
Bacteria developing resistance to antibiotics
The beak sizes of ground finches on Daphne Island

23. Directional Selection
Imagine that the environment changes and the supply of small and medium-sized seeds runs low. Which beak size will be favored?
Those birds with the larger beak will be able to survive on the large seeds!
In “directional selection,” natural selection favors a characteristic on the extreme of the phenotypic variation.
How does this affect variation?
Variation of beak size shifts in ONE direction.

24. Directional Selection
Original distribution of beak sizes
How distribution of beak sizes change due to a changing environment

25. What is Stabilizing Selection?
In “stabilizing selection,” natural selection favors characteristics near the middle (average) of the phenotypic distribution.
Occurs when the environment is stable for long periods
Example height variation in humans
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26. Stabilizing Selection
Imagine that the environment changes and the supply of small and large-sized seeds runs low. Which beak size will be favored now?
Those birds with the medium beak will be able to survive on the medium seeds!
In “stabilizing selection,” natural selection favors characteristics near the middle of the phenotypic distribution.
How does this affect variation?
Variation of beak size shifts in towards the middle, decreasing genetic variation at the extremes.

27. Stabilizing Selection

28. What is Disruptive Selection?
In “disruptive selection,” natural selection selects against the average and favors characteristics at BOTH extremes of the phenotypic variation.
Example: variations in height in weeds of lawns and in the wild.
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29. Disruptive Selection
How distribution of beak sizes change due to a changing environment
Original distribution of beak sizes

30. African Seed Crackers Birds feed on two types of seeds one
large, one small.
Birds with average
size bills can’t eat
either type efficiently
And so aren’t common
in the population

31. Disruptive Selection
Imagine that the environment changes and only the supply of medium-sized seeds runs low. Which beak size will be favored now?
Those birds with BOTH the smaller and larger beak will be able to survive!
In “disruptive selection,” natural selection favors characteristics at BOTH extremes of the phenotypic variation.
How does this affect variation?
Variation shifts to favor two subgroups of birds specialized in eating different sized seeds.

32. Natural Selection on Polygenic Traits

33. Natural Selection in a Nutshell
Differences in phenotype leads to differences in the success rate of organisms to reproduce.
Those phenotypes which are better suited to their environment, have more reproductive success
Natural Selection acts on phenotype to change the gene pool

34. Natural Selection
all of the genes in a population are referred to as the population’s gene pool
Over time, the selection of phenotypes,
changes the frequency with which alleles occur in a population’s gene pool
- the alleles for advantageous traits become more common, while alleles for harmful traits become less common

35. Evolution as Genetic Change
Let’s imagine Darwin’s finches on the Galapagos Islands as an example.
There is slight variation in beak length among the finches, ranging from…
-small beaks (for obtaining small seeds)
-medium beaks (for obtaining medium seeds)
-large beaks (for harder, thick-shelled seeds)